2 foot ball of solid yellow light passed me four feet away and six feet off the ground.no sound or heat

I was driving down a highway on my way home and saw this ball of light coming down the middle of the road. At first I thought It was a motorcycle head light in the distance. When it got closer, I slowed down to let it go by because it was right on the yellow line.

When it was about 100 meters or better I saw that it was just a ball of light and nothing else. It passed me about six off the ground and was just a sphere of light about the size of a large medicine ball about two feet in diameter. I watched it in my mirror as it disappeared down the road. I slowed down to about 50 KPH (30MPH) and it maintained its speed. It wasn't moving very fast maybe 100 KPH (60MPH).

I looked for reasons such as on coming traffic or lights from any where. There was nothing in the sky ,it was daylight and there were no other vehicles coming my way or behind me.